Implement ColorToSolidColorBrushConverter

src/MahApps.Metro/Converters/ColorToSolidColorBrushConverter.cs

@@ -0,0 +1,51 @@
+using System;
+using System.Globalization;
+using System.Windows.Data;
+using System.Windows.Media;
+using JetBrains.Annotations;
+
+namespace MahApps.Metro.Converters
+{
+    /// <summary>
+    /// Converts a given <see cref="Color"/> into a <see cref="SolidColorBrush"/>.
+    /// </summary>
+    [ValueConversion(typeof(Color), typeof(SolidColorBrush))]
+    public class ColorToSolidColorBrushConverter : IValueConverter
+    {
+        private static ColorToSolidColorBrushConverter defaultInstance;
+
+        /// <summary>
+        /// Gets a static instance of the converter if needed.
+        /// </summary>
+        public static ColorToSolidColorBrushConverter DefaultInstance => defaultInstance ??= new ColorToSolidColorBrushConverter();
+
+        /// <summary>
+        /// Gets or Sets the brush which will be used if the conversion fails.
+        /// </summary>
+        [CanBeNull]
+        public SolidColorBrush FallbackBrush { get; set; }
+
+        /// <summary>
+        /// Gets or Sets the color which will be used if the conversion fails.
+        /// </summary>
+        [CanBeNull]
+        public Color? FallbackColor { get; set; }
+
+        public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
+        {
+            if (value is Color color)
+            {
+                var brush = new SolidColorBrush(color);
+                brush.Freeze();
+                return brush;
+            }
+
+            return this.FallbackBrush;
+        }
+
+        public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
+        {
+            return value is SolidColorBrush brush ? brush.Color : this.FallbackColor;
+        }
+    }
+}

src/MahApps.Metro/Themes/ColorPicker/ColorCanvas.xaml

@@ -187,11 +187,7 @@
                                         Background="{DynamicResource MahApps.Brushes.Tile}"
                                         BorderBrush="{DynamicResource MahApps.Brushes.ThemeForeground}"
                                         BorderThickness="1">
-                                    <Rectangle>
-                                        <Rectangle.Fill>
-                                            <SolidColorBrush Color="{Binding RelativeSource={RelativeSource Mode=TemplatedParent}, Path=SelectedColor, TargetNullValue=Transparent}" />
-                                        </Rectangle.Fill>
-                                    </Rectangle>
+                                    <Rectangle Fill="{Binding RelativeSource={RelativeSource TemplatedParent}, Path=SelectedColor, Converter={x:Static converters:ColorToSolidColorBrushConverter.DefaultInstance}}" />
                                 </Border>
 
                                 <ContentControl x:Name="PART_NoColorPreview"

src/MahApps.Metro/Themes/ColorPicker/ColorPalette.xaml

@@ -111,11 +111,7 @@
                     <Binding Path="ColorNamesDictionary" RelativeSource="{RelativeSource Mode=FindAncestor, AncestorType=mah:ColorPalette}" />
                 </MultiBinding>
             </Border.ToolTip>
-            <Grid>
-                <Grid.Background>
-                    <SolidColorBrush Color="{Binding}" />
-                </Grid.Background>
-            </Grid>
+            <Grid Background="{Binding Converter={x:Static converters:ColorToSolidColorBrushConverter.DefaultInstance}}" />
         </Border>
     </DataTemplate>
 

src/MahApps.Metro/Themes/ColorPicker/ColorPicker.xaml

@@ -22,11 +22,7 @@
                     Background="{DynamicResource MahApps.Brushes.Tile.Small}"
                     BorderBrush="{DynamicResource MahApps.Brushes.Control.Border}"
                     BorderThickness="1">
-                <Rectangle>
-                    <Rectangle.Fill>
-                        <SolidColorBrush Color="{Binding TargetNullValue=Transparent}" />
-                    </Rectangle.Fill>
-                </Rectangle>
+                <Rectangle Fill="{Binding Converter={x:Static converters:ColorToSolidColorBrushConverter.DefaultInstance}}" />
             </Border>
 
             <TextBlock Grid.Column="1"
@@ -49,11 +45,7 @@
                 Background="{DynamicResource MahApps.Brushes.Tile.Small}"
                 BorderBrush="{DynamicResource MahApps.Brushes.Control.Border}"
                 BorderThickness="1">
-            <Rectangle>
-                <Rectangle.Fill>
-                    <SolidColorBrush Color="{Binding}" />
-                </Rectangle.Fill>
-            </Rectangle>
+            <Rectangle Fill="{Binding Converter={x:Static converters:ColorToSolidColorBrushConverter.DefaultInstance}}" />
         </Border>
         <DataTemplate.Triggers>
             <DataTrigger Binding="{Binding}" Value="{x:Null}">